Category: Broadcast Radio

rtl_icecast: A Terminal Application for Streaming FM to an Icecast Server with RTL-SDR

Thank you to Jouni (OH3CUF) for submitting news about the recent release of his new Linux terminal based open-source software called 'rtl_icecast', which can be used with an RTL-SDR to stream FM audio to an Icecast server.

Icecast is an open-source streaming media server that broadcasts audio and video streams over the internet.

Jouni writes:

rtl_icecast is a shell native application that uses RTL-SDR to receive FM radio signals and stream them to an Icecast server in MP3 format.

The main target usage for this app is to stream your local HAM FM repeater audio to your public shoutcast/icecast server with just a RTL-SDR USB-receiver and for example Raspberry Pi. It can be used to stream broadcast FM too, of course.

The app is native app and uses the RTL-SDR on hardware level directly. No need to pipe or install anything extra. This works out of the box (well, I hope!)."

A block diagram of how the rtl_icecast streamer works
A block diagram of how the rtl_icecast streamer works

The Taylorator: Flooding the Broadcast FM Band with Taylor Swift Songs using a LimeSDR

Over on Hackaday and creator Stephen's blog, we've seen an article about the 'Taylorator,' open source software for the LimeSDR that floods the broadcast FM band with Taylor Swift music. In his blog post, Stephen explains how he wrote this software, explaining the concepts behind audio preparation, FM modulation, and what computing hardware was required to implement it.

The advertised use case of the Taylorator is obviously a bit of a joke; however, as the video on Stephen's blog shows, his software can play a different song on every broadcast FM channel. So, there could be some use cases where you might want people to be able to tune an FM radio to custom music on each channel. Of course, you could also just use it to play a practical joke on someone.

In terms of legality, in his blog post, Stephen notes that blasting the broadcast FM band on every channel is probably not legal and may go against the spirit of low-power FM transmitter laws in most countries. However, he notes that spreading a few mW over 20 MHz of bandwidth results in a weak signal that is unlikely to travel very far. Regardless, we would advise potential users of the software to check their local laws before going ahead and playing around with something like this.

The software is open source and available on Stephen's GitLab.

The Taylorator: Broadcasting Taylor Swift songs on every broadcast FM channel
The Taylorator: Broadcasting Taylor Swift songs on every broadcast FM channel

Guglielmo FM and DAB Receiver Software Updated to Version 0.6

Thank you to Marco, Guglielmo's programmer, for letting us know that his software has recently been updated to Version 0.6.

Guglielmo is Linux, Windows (and, in this recent update, x86 MacOS) based RTL-SDR FM and DAB tuner software that supports SDRs, including the RTL-SDR, Airspy, SDRplay, HackRF, and LimeSDR. It is designed to be easy to use for media users rather than hobbyist technical users.

Version 0.6 fixes bugs and adds the following features:

  • Software automatic gain control
  • Support for multiple devices for RTL-SDR and SDRplay
  • Support for RTL-SDR V4
  • New RTL-SDR and SDRPlay device drivers
  • New Portaudio sound driver
Guglielmo: Screenshot of the DAB Interface

Updates to the Lego Pi Radio Project

Back in 2018 we first posted about JJ's Lego Pi Radio, which was an all-in-one RTL-SDR + Raspberry Pi based FM and internet radio system enclosed in Lego.

More recently JJ has written in again sharing with us some updates to his Lego Pi project. First, he notes that he has now created a webpage showing all his radio builds, most of which consist of an Arduino Nano + Raspberry Pi and RTL-SDR, with most enclosed in Lego builds.

JJ also wanted to highlight his latest build optimized for DAB reception, made from an old Android TV box, RTL-SDR the welle-cli software, and of course a Lego enclosure.

My latest build, a FM / DAB+ / INTERNET / MP3 radio, was not made with a Raspberry Pi but with an older Android TV box flashed with Armbian + Ubuntu.
 
This was cheaper and allowed me to recycle some hardware that was gathering dust. Besides the board needs less power and best of all, the whole system fits into internal eMMC storage, so no more messing with fragile micro SD card. The only problem I had was with the onboard audio so had to use an inexpensive USB audio dongle. I also connected an Arduino nano through USB to easily control a small LCD display and some LEDs.
 
The board's IR port works well under Linux so I can control the radio with any cheap infrared remote. But I also made a web interface for a fun way to drive the radio from a tablet, PC or even smartphone.
The Lego Android RTL-SDR Build
Lego Android RTL-SDR Build
Lego Android RTL-SDR Build Web Interface

Exploring HD Radio and Other Signals While on Holiday

Over on his YouTube channel, Simon has uploaded a video showing how while on holiday he was able to explore the various HD Radio stations available around the USA. 

If you are in the USA, you might recognize HD Radio (aka NRSC-5) signals as the rectangular looking bars on the frequency spectrum that surround common broadcast FM radio signals. These signals only exist in the USA and they carry digital audio data which can be received by special HD Radio receivers. Earlier in 2017 a breakthrough in HD Radio decoding for SDRs like the RTL-SDR was achieved by Theori when he was able to piece together a full HD Radio software audio decoder that works in real-time. Nowadays you can use software like HDFM - HD Radio GUI to easily receive HD Radio with an RTL-SDR.

In his video Simon shows the various HD Radio signals he found while on holiday, and also shows some of their secondary features, including traffic data, and weather radar maps. Interestingly he also spots HD Radio in the AM bands, but finds his signal is not strong enough to decode.

The rest of the video explores other signals he finds such as a studio link, and TV audio signals.

I Found Some CRAZY Radio Technology while Traveling!

Testing DAB Decoders: SDRAngel versus Welle.io

Thank you to the team from DXing.org for submitting their video where they compare the DAB decoding performance of SDRAngel and Welle.io using an RTL-SDR Blog V3 dongle.

Digital Audio Broadcast (DAB) is a digital replacement for analog broadcast FM. It provides high quality digital audio at the expense of higher cost receivers, and possibly greater difficulty with reception in weak or challenging RF environments. DAB is mostly only used in Europe and Asia Pacific regions, and is not found in the USA. SDRAngel and Welle.io are both RTL-SDR compatible programs with DAB decoding capabilities. Both can run on Android, PC, MacOS and Linux devices.

In their tests they find that the Welle.io DAB decoder works perfectly without issues, however the SDRAngel DAB decoder struggles and has difficulty with decoding. Given that Welle.io is a dedicated DAB decoder, and SDRAngel is a multipurpose tool this could be expected. But we are unsure what is wrong with the DAB implementation in SDRAngel.

The team note that the test was carried out in Sofia, Bulgaria, Europe, using a Serbian DAB+ signal from Yastrebac, with a distance of 175km.

Test android apps with DAB+ signal Welle.io vs. SDRangel, receiver rtl-sdr v.3

Guglielmo FM and DAB Receiver Software Updated to Version 0.5

Thank you to Marco, the programmer of Guglielmo for letting us know that his software has recently been updated to Version 0.5.

Guglielmo is a Linux, Windows (and in this recent update x86 MacOS) based RTL-SDR FM and DAB tuner software that supports SDRs including the RTL-SDR, Airspy, SDRplay, HackRF and LimeSDR. It is designed to be an easy to use program designed for media users, rather than hobbyist technical users.

Regarding the release of Version 0.5, Marco writes:

This release sports full mac (x86 only, sorry) and windows installers, DAB and FM scans and a preset editor.

Guglielmo: Screenshot of the DAB Interface

SDRangel Now Available on Android: Mobile ADS-B, AIS, APT, Digital Voice, POCSAG, APRS, RS41 Radiosonde Decoders

SDRangel is a free open source software defined radio program that is compatible with many SDRs, including RTL-SDRs. SDRAngel is set apart from other programs because of it's huge swath of built in demodulators and decoders.

Thank you to reader Jon for writing in and noting that SDRangel has recently been released for Android as a free Google Play download. This is an amazing development that could open up many doors into portable decoding setups as the Android version supports almost every decoder implemented on the desktop version. Jon writes:

It includes most of the functionality of the desktop version of SDRangel, including:

  • AM, FM, SSB, Broadcast FM and DAB, AIS, ADS-B, Digital Voice (DMR, dPMR, D-Star, FreeDV), Video (DVB-S, DVB-S2, NTSC, PAL), VOR, LoRa, M17, Packet (AX.25), Pager (POCSAG), Radiosonde (RS41), Time signal (MSF, DCF77, TDF and WWVB) modems.
  • RTL SDR, Airspy, Airspy HF, LimeSDR, HackRF and SDRplay support via USB OTG as well as networked SDRs
  • 2D and 3D signal analysis in both time and frequency domain with statistical measurements of SNR, THD, THD+N, SINAD, SFDR and channel power
  • Satellite tracker, star tracker, maps and rotator controller

It should work on Android 6 and up. It’s a straight port of the desktop application, so although it will run on a phone, probably best used on a large tablet with a stylus or mouse.

SDRangel on Android
SDRangel on Android
SDRangel